Clock, Frequency Reference, and Other Reference Signal Generator with Frequency Stability Over Temperature Variation

• US 20100271144A1
• Filed: 04/23/2010
• Published: 10/28/2010
• Est. Priority Date: 04/24/2009
• Status: Active Grant

• Current Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Original Assignee: Integrated Device Technology Incorporated (Renesas Electronics Corporation)
• Inventors: Gupta, Vidyabhusan, Gaskin, Nathaniel Charles, Fayyaz, Nader, McCorquodale, Michael Shannon, Pernia, Scott Michael
• Granted Patent: US 8,134,414 B2
• Time in Patent Office: Days
• US Class Current: 331/117.FE
• CPC Class Codes: H03B 5/04 Modifications of generator to compensate for variations in physical values, e.g. power supply, load, temperature
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1271 the frequency being controlled by a control current, i.e. current controlled oscillators
• CPC Class Codes: H03B 5/1293 having means for achieving a desired tuning characteristic, e.g. linearising the frequency characteristic across the tuning voltage range

Abstract

Exemplary embodiments provide a reference signal generator having a reference or center frequency within a predetermined variance over variations in temperature within a specified range. An exemplary apparatus comprises a reference resonator to generate a first reference signal having a resonant frequency, with the reference resonator having a first temperature dependence; and a plurality of switchable circuits, with at least one switchable circuit providing a second temperature dependence opposing the first temperature dependence to maintain the resonant frequency within a predetermined variance over a temperature variation. A wide variety of switchable circuits are disclosed, including a transistor having an on resistance value greater than a nominal resistance, a resistor coupled to a transistor or other switch, and circuit comprising a first reactance coupled to a first switch, with a second reactance coupled to a resistance and a second switch coupled in series to the second reactance or to the resistance. Various coatings may also be applied to an integrated circuit embodiment, such as a silicone coating on a first surface and a metal layer on a second surface.

Claims

1. An apparatus to generate a harmonic reference signal, the apparatus comprising:

a reference resonator to generate a first reference signal having a resonant frequency, the reference resonator comprising a first component having a first temperature dependence; and

a plurality of switchable circuits couplable to the reference resonator, at least one switchable circuit of the plurality of switchable circuits having a second temperature dependence opposing the first temperature dependence to maintain the resonant frequency within a predetermined variance over a temperature variation.

2. The apparatus of claim 1, wherein each switchable circuit of the plurality of switchable circuits comprises:

a first reactance;

a resistance; and

a second reactance coupled to the resistance.

3. The apparatus of claim 2, wherein each switchable circuit of the plurality of switchable circuits further comprises:

a first switch coupled in series to the first reactance; and

a second switch coupled in series to the second reactance or to the resistance.

4. The apparatus of claim 3, wherein the first switch is responsive to a control signal of a plurality of control signals to electronically couple or decouple the first reactance to or from a voltage, a ground potential, or the reference resonator.

5. The apparatus of claim 4, wherein the second switch is responsive to an inverted control signal of a plurality of control signals to electronically couple or decouple the second reactance or the resistance to or from a voltage, a ground potential, or the reference resonator.

6. The apparatus of claim 4, wherein the plurality of control signals are determined during a temperature calibration process over a predetermined range of temperature variation to determine selected resistances of the plurality of switchable circuits to be coupled to the reference resonator to provide the second temperature dependence to maintain the resonant frequency within the predetermined variance.

7. The apparatus of claim 3, further comprising:

a coefficient register to store a plurality of control coefficients;

wherein the first switch is responsive to a control coefficient of the plurality of control coefficients to electronically couple or decouple the first reactance to or from a voltage, a ground potential, or the reference resonator, and wherein the second switch is responsive to an inverted control coefficient of the plurality of control coefficients to electronically couple or decouple the second reactance or the resistance to or from a voltage, a ground potential, or the reference resonator.

8. The apparatus of claim 7, wherein the plurality of control coefficients are determined during a temperature calibration process over a predetermined range of temperature variation to determine selected resistances of the plurality of switchable circuits to be coupled to the reference resonator to provide the second temperature dependence to maintain the resonant frequency within the predetermined variance.

9. The apparatus of claim 2, wherein the second reactance coupled to the resistance has the second temperature dependence opposing the first temperature dependence.

17. The apparatus of claim 1, further comprising:

a frequency controller coupled to the reference resonator, the frequency controller to maintain substantially constant a peak amplitude of the first reference signal and a common mode voltage level of the reference resonator.

18. The apparatus of claim 17, further comprising:

a first variable current source to provide a current to the reference resonator; and

wherein the frequency controller is further to generate a first control signal to the first variable current source to modify the current to the reference resonator to maintain the peak amplitude of the first reference signal substantially constant at a predetermined magnitude.

19. The apparatus of claim 18, wherein the frequency controller further comprises:

an amplitude detector to detect a magnitude of the peak amplitude of the first reference signal; and

an operational amplifier coupled to the amplitude detector and the first current source, the operational amplifier to generate the first control signal to the first variable current source to modify the current level when the detected magnitude is not substantially equal to the predetermined magnitude.

20. The apparatus of claim 18, wherein the frequency controller further comprises:

an amplitude detector to detect a magnitude of the peak amplitude of the first reference signal; and

a comparator coupled to the amplitude detector and the first variable current source, the comparator to generate the first control signal to the first variable current source to modify the current level when the detected magnitude is not substantially equal to the predetermined magnitude.

21. The apparatus of claim 17, further comprising:

a second variable current source to provide the current to the reference resonator; and

wherein the frequency controller is further to generate a second control signal to the second variable current source to modify the current to the reference resonator to maintain the common mode voltage level of the reference resonator substantially constant at a predetermined voltage level.

22. The apparatus of claim 21, wherein the frequency controller further comprises:

a voltage detector to detect the common mode voltage level of the reference resonator; and

an operational amplifier coupled to the voltage detector and the second variable current source, the operational amplifier to generate the second control signal to the second variable current source to modify the current level when the detected common mode voltage level is not substantially equal to the predetermined common mode voltage level.

23. The apparatus of claim 21, wherein the frequency controller further comprises:

a voltage detector to detect the common mode voltage level of the reference resonator; and

a comparator coupled to the voltage detector and the second variable current source, the comparator to generate the second control signal to the second variable current source to modify the current level when the detected common mode voltage level is not substantially equal to the predetermined common mode voltage level.

24. The apparatus of claim 1, further comprising:

a plurality of variable capacitors coupled to the reference resonator to modify a corresponding reactance in response to a control voltage to maintain the resonant frequency substantially constant.

10-16. -16. (canceled)

25. An apparatus to generate a harmonic reference signal, the apparatus comprising:

a reference resonator to generate a first reference signal having a resonant frequency, the reference resonator having a first temperature dependence, the reference resonator comprising an inductor and a capacitor; and

a plurality of switchable resistance circuits couplable to the reference resonator, and when coupled to the reference resonator, at least one switchable resistance circuit of the plurality of switchable resistance circuits providing a second temperature dependence opposing the first temperature dependence to maintain the resonant frequency within a predetermined variance.

26-49. -49. (canceled)

50. A reference oscillator apparatus, the apparatus comprising:

a reference resonator to generate a first reference signal having a resonant frequency, the reference resonator having a first temperature dependence;

a plurality of switchable circuits couplable to the reference resonator, and when coupled to the reference resonator, at least one switchable circuit of the plurality of switchable circuits providing a second temperature dependence opposing the first temperature dependence to maintain the resonant frequency within a predetermined variance over a temperature variation; and

at least one feedback circuit coupled to the reference resonator, the at least one feedback circuit to maintain substantially constant a peak amplitude of the first reference signal or a common mode voltage level of the reference resonator.

51-131. -131. (canceled)